1. Field of the Invention
The present invention relates generally to ultrasonic metal inspection and more particularly, to an ultrasonic search system of the type in which a plurality of ultrasonic sensors or probes transmit ultrasonic waves into a test piece of a circular section to determine the presence of flaws by reflections while a probe holder is being rotated about the axis of the test piece.
2. Description of the Related Art
Various ultrasonic search or metal inspection systems have been proposed to scan a test piece such as a steel pipe or a round rod so as to detect flaws in the test piece. An exemplary prior art ultrasonic search system is disclosed in Japanese Laid-Open Utility Model Application No. 66863/81 and includes an inner sleeve or nozzle block through which a test piece passes. An outer sleeve or probe holder is disposed in coaxial relation to the nozzle block so as to define an annular space or passage therebetween. The nozzle block and the probe holder are both driven for rotation around the test piece. A plurality of ultrasonic sensors, commonly referred to as a probe, extend radially through the probe holder and into the passage. The nozzle block has a plurality of nozzle openings in radial alignment with the probes. While the probe holder and the probes are rotated at a high speed, water under pressure is introduced into the annular passage and then, injected from the nozzle openings toward the test piece to form a water column. Ultrasonic waves are transmitted from the probes through the water column into the test piece. Now that the probes are rotated about the axis of the elongate test piece, the test piece can be scanned in a spiral fashion. This metal inspection method enables rapid and accurate scanning or inspection of a test piece of a circular section.
When the probe holder is rotated at a high speed, for example 1,000 r.p.m., the resulting centrifugal force causes water to leak from a portion of the probe holder to which the probes are secured. It will be appreciated that a water column must be maintained between each probe and a test piece to provide an acoustic coupling therebetween. To prevent water leakage, attempts have been made to more firmly secure the probes to the probe holders with a larger number of screws or similar means. However, this results in an increase in the time required to replace the existing probes. Such replacement is required when a new test piece of a different diameter is to be inspected.